Supporting additional VSU edge cases

core/vb.c

@@ -29,6 +29,7 @@ typedef struct {
 
         /* Other state */
         uint32_t clocks;  /* Clocks until modification */
+        uint8_t  modmask; /* Modifications masked */
         uint8_t  reload;  /* Automatic reload value */
     } env;
 
@@ -360,6 +361,7 @@ struct VB {
 
             /* Other state */
             uint32_t clocks;  /* Clocks until modification */
+            uint8_t  modmask; /* Modifications masked */
             uint16_t next;    /* Next frequency value */
             int      sample;  /* Current sample index */
         } freqmod;

core/vsu.c

@@ -45,9 +45,22 @@ static void vsuOnSamples(VB *sim) {
 
 /***************************** Module Functions ******************************/
 
+/* Determine while frequency modifications should be processed */
+static uint8_t vsuCheckFreqMod(VB *sim) {
+    return
+        sim->vsu.freqmod.enb           &&
+        sim->vsu.freqmod.interval != 0 && (
+            !sim->vsu.freqmod.modmask || (
+                sim->vsu.freqmod.func == 1 &&
+                sim->vsu.freqmod.rep
+            )
+        )
+    ;
+}
+
 /* Stage the next frequency modification value */
 static void vsuNextFreqMod(VB *sim, Channel *chan) {
-    uint16_t next;
+    int32_t next;
 
     /* Sweep */
     if (sim->vsu.freqmod.func == 0) {
@@ -57,18 +70,34 @@ static void vsuNextFreqMod(VB *sim, Channel *chan) {
         else next = chan->freq.current + next;
         if (next > 2047)
             chan->int_.enb = 0;
+        if (next < 0)
+            next = 0;
     }
 
     /* Modulation */
     else {
-        next = (chan->freq.written +
+
-            sim->vsu.modulation[sim->vsu.freqmod.sample]) & 2047;
+        /* Compute the modulated value */
+        next = (int32_t) chan->freq.written +
+            sim->vsu.modulation[sim->vsu.freqmod.sample];
+        if (next < 0)
+            next = 0;
+        if (next > 2047)
+            next = 2047;
+
+        /* Not the final modulation sample */
         if (sim->vsu.freqmod.sample != 31)
             sim->vsu.freqmod.sample++;
-        else if (sim->vsu.freqmod.rep)
+
+        /* Last modulation sample processed */
+        else {
+            sim->vsu.freqmod.modmask = 1;
+            if (sim->vsu.freqmod.rep)
                 sim->vsu.freqmod.sample = 0;
         }
 
+    }
+
     /* Configure state */
     sim->vsu.freqmod.next = next;
 }
@@ -106,13 +135,14 @@ static void vsuEmulateChannel(VB *sim, Channel *chan) {
     }
 
     /* Envelope modification */
-    if (chan->env.enb && chan->env.clocks == 0) {
+    if (chan->env.enb && !chan->env.modmask && chan->env.clocks == 0) {
         if (chan->env.dir == 0 && chan->env.value != 0)
             chan->env.value--;
         else if (chan->env.dir == 1 && chan->env.value != 15)
             chan->env.value++;
         else if (chan->env.rep)
             chan->env.value = chan->env.reload;
+        else chan->env.modmask = 1;
         chan->env.clocks = ((uint32_t) chan->env.interval + 1) * 307220;
     }
 
@@ -186,9 +216,8 @@ static void vsuWriteEV1(VB *sim, int index, uint8_t value) {
             sim->vsu.freqmod.enb  = value >> 6 & 1;
             sim->vsu.freqmod.func = value >> 4 & 1;
             sim->vsu.freqmod.rep  = value >> 5 & 1;
+            chan->freqmod         = vsuCheckFreqMod(sim);
             vsuNextFreqMod(sim, chan);
-            chan->freqmod =
-                sim->vsu.freqmod.enb && sim->vsu.freqmod.interval != 0;
             break;
 
         case 5: /* Channel 6 */
@@ -228,6 +257,7 @@ static void vsuWriteINT(VB *sim, int index, uint8_t value) {
 
     /* Update state */
     chan->int_.clocks = 76805 * ((uint32_t) chan->int_.interval + 1);
+    chan->env.modmask = 0;
     if (chan->env.enb)
         chan->env.clocks = 307220 * ((uint32_t) chan->env.interval + 1);
     if (index != 5) {
@@ -240,6 +270,7 @@ static void vsuWriteINT(VB *sim, int index, uint8_t value) {
     if (index == 4) {
         sim->vsu.freqmod.clocks = (uint32_t) sim->vsu.freqmod.interval *
             (sim->vsu.freqmod.clk == 0 ? 19200 : 153600);
+        sim->vsu.freqmod.modmask = 0;
         sim->vsu.freqmod.sample  = 0;
     }
 
@@ -272,8 +303,7 @@ static void vsuWriteSWP(VB *sim, uint8_t value) {
         (sim->vsu.freqmod.clk == 0 ? 19200 : 153600);
     if (clocks < sim->vsu.freqmod.clocks)
         sim->vsu.freqmod.clocks = clocks;
-    sim->vsu.channels[4].freqmod =
+    sim->vsu.channels[4].freqmod = vsuCheckFreqMod(sim);
-        sim->vsu.freqmod.enb && sim->vsu.freqmod.interval != 0;
 }
 
 
@@ -315,7 +345,8 @@ static void vsuEmulate(VB *sim, uint32_t clocks) {
 
                     /* Clocks until next state change */
                     chan->until = chan->clocks;
-                    if (chan->env.enb && chan->env.clocks < chan->until)
+                    if (chan->env.enb && !chan->env.modmask &&
+                        chan->env.clocks < chan->until)
                         chan->until = chan->env.clocks;
                     if (chan->int_.auto_ && chan->int_.clocks < chan->until)
                         chan->until = chan->int_.clocks;
@@ -324,7 +355,7 @@ static void vsuEmulate(VB *sim, uint32_t clocks) {
 
                     /* Manage clocks */
                     chan->clocks -= chan->until;
-                    if (chan->env.enb)
+                    if (chan->env.enb && !chan->env.modmask)
                         chan->env.clocks -= chan->until;
                     if (chan->int_.auto_)
                         chan->int_.clocks -= chan->until;
@@ -427,6 +458,7 @@ static void vsuReset(VB *sim) {
         chan->env.enb       = 0;
         chan->env.dir       = 0;
         chan->env.interval  = 0;
+        chan->env.modmask   = 0;
         chan->env.reload    = 0;
         chan->env.rep       = 0;
         chan->env.value     = 0;
@@ -449,6 +481,7 @@ static void vsuReset(VB *sim) {
     sim->vsu.freqmod.enb      = 0;
     sim->vsu.freqmod.func     = 0;
     sim->vsu.freqmod.interval = 0;
+    sim->vsu.freqmod.modmask  = 0;
     sim->vsu.freqmod.next     = 0;
     sim->vsu.freqmod.rep      = 0;
     sim->vsu.freqmod.sample   = 0;